Simulation of Grover's Quantum Database Search Algorithm

I have a basic understanding of Grover's algorithm, and I do know it searches through an unstructured database for some value. I recently downloaded the Quantum Processing Simulation (QPS), and after trying out the Grover simulator I became confused: through what database is it searching? It asks for the number you wish to search for, but then it just spits that number back at you. From where exactly is it retrieving this number from?
It greatly confused me....any clarification would be great.

I don't know the simulation software you try, but Grover's algorithm searches through values computable by mean of operations on qubits. So it is more finding a reverse function than searching database.

You must provide a test routine, telling if the proposed index is right or not. This routine must be computable in quantum way (on a suporposition of states). Grover's algorithm finds matching index.

Frankly: I would also want to know how complicated the functions may be to be feasible to implement using current technology.